Of the Son of God as Neither Made by the Father Nor Less Than the Father, and of His Incarnation
9 Moreover, those parties also are to be abhorred who deny that our Lord Jesus Christ had in Mary a mother upon earth; while that dispensation has honored both sexes, at once the male and the female, and has made it plain that not only that sex which He assumed pertains to God's care, but also that sex by which He did assume this other, in that He bore [the nature of] the man (virum gerendo), [and] in that He was born of the woman. Neither is there anything to compel us to a denial of the mother of the Lord, in the circumstance that this word was spoken by Him: “Woman, what have I to do with you? Mine hour is not yet come.” But He rather admonishesus to understand that, in respect of His being God, there was no mother for Him, the part of whose personal majesty (cujus majestatis personam) He was preparing to show forth in the turning of water into wine. But as regards His being crucified, He was crucified in respect of his being man; and that was the hour which had not come as yet, at the time when this word was spoken, “What have I to do with you? Mine hour is not yet come;” that is, the hour at which I shall recognize you. For at that period, when He was crucified as man, He recognized His human mother (hominem matrem), and committed her most humanely (humanissime) to the care of the best beloved disciple. Nor, again, should we be moved by the fact that, when the presence of His mother and His brethren was announced to Him, He replied, “Who is my mother, or who my brethren?” etc. But rather let it teach us, that when parents hinder our ministry wherein we minister the word of God to our brethren, they ought not to be recognized by us. For if, on the ground of His having said, “Who is my mother?” every one should conclude that He had no mother on earth, then each should as matter of course be also compelled to deny that the apostles had fathers on earth; since He gave them an injunction in these terms: “Call no man your father upon the earth; for one is your Father, which is in heaven.”
10. Neither should the thought of the woman's womb impair this faith in us, to the effect that there should appear to be any necessity for rejecting such a generation of our Lord for the mere reason that worthless men consider it unworthy (sordidi sordidam putant). For most true are these sayings of an apostle, both that “the foolishness of God is wiser than men,” and that “to the pure all things are pure.” Those, therefore, who entertain this opinion ought to ponder the fact that the rays of this sun, which indeed they do not praise as a creature of God, but adore as God, are diffused all the world over, through the noisomenesses of sewers and every kind of horrible thing, and that they operate in these according to their nature, and yet never become debased by any defilement thence contracted, albeit that the visible light is by nature in closer conjunction with visible pollutions. How much less, therefore, could the Word of God, who is neither corporeal nor visible, sustain defilement from the female body, wherein He assumed human flesh together with soul and spirit, through the incoming of which the majesty of the Word dwells in a less immediate conjunction with the frailty of a human body! Hence it is manifest that the Word of God could in no way have been defiled by a human body, by which even the human soul is not defiled. For not when it rules the body and quickens it, but only when it lusts after the mortal good things thereof, is the soul defiled by the body. But if these persons were to desire to avoid the defilements of the soul, they would dread rather these falsehoods and profanities.
Source: On Faith and the Creed (New Advent)